When sensors are employed in the detection of biological materials in a particular environment, it is sometimes necessary to be able to detect refractive index changes within a certain range. Therefore, it is desirable to be able to tailor the fabrication of the optical sensor to be sensitive to a specific refractive index range. This has been accomplished in the past by applying coatings to the surface of the optical sensor. In particular, Murphy et al. (U.S. Pat. No. 5,864,641) disclose an optical fiber long period grating sensor having a reactive coating positioned in an operable relationship to the long period grating wherein the reactive coating causes the long period grating to produce a wavelength transmission spectrum functionally dependent on a sensed parameter. They describe the coating as being either physically reactive, electrically reactive, or chemically reactive. More specifically, the chemically reactive coating is described as one which undergoes a chemical change when exposed to certain target materials. The reaction may either change the chemical or physical composition of the coating. For example, when the chemically reactive coating has target sites present, a chemical bond is formed between the target site and a specific molecule. In this instance, there is a change in the wavelength transmission spectrum produced by the long period grating which results from exposure of the reactive coating to certain substances. They describe the coating as a concentrated solution of a material having active sites, such as antibodies, which are deposited directly on the waveguide so the active sites attach directly to the waveguide. Alternatively, the coating may be a complex formulation having other materials compounded along with the material with the active sites such that the active sites are attached within the coating. Specifically, these active sites are described as low molecular weight ligands. When the coating is deposited on the waveguide, the active sites are oriented away from the waveguide so they are able to complex with specific target molecules. The coating may also be compounded to have the active sites undergo a change in the physical property of the coating when in comes in contact with a specific material. In this instance, the coating may be solvated by a specific solvent, thus causing the thickness of the coating to change which ultimately changes the coating's refractive index profile. Lastly, the coating is described as one which may have active sites which bond with fluorescent dyes. In all instances, the reactive coating is described as one capable of producing a wavelength transmission spectrum functionally dependent on a specific parameter which is sensed. However, the coatings described by Murphy et al. are deficient for applications requiring high sensitivity within a specific refractive index range.
An object of the present invention is to provide a biosensor that has a coating having a refractive index that is tailored to enhance the sensitivity of the biosensor to an environmental parameter.
Another object of the invention is to provide a biosensor that has a coating having a refractive index ranging from about 1.0 to about 1.5.
Another object of the present invention is to provide a biosensor that has a coating which permits enhanced sensitivity, an operational wavelength that may be tailored to the application, and has increased binding capacity.
Another object of the present invention is to provide a method of fabrication of a biosensor which has a coating having a refractive index ranging from about 1.0 to about 1.5.